Safe recovery of tetrahydrofuran vapors



'this spec fication.

SAFE RECOVERY on TETRAHYDROFURAN VAPORS Paul F. Bente, Jr., Lewiston, N. Y.,

Pont de Nemours and Company, Wilmington, corporation of Delaware No Drawing Application February 25, 1953,

Serial No. 338,871

12 Claims. 01. 260-3461) Del., :1

This invention relates to the recovery of tetrahydrofuran vapors fromair and more particularly to therecovery of the vapors without the formation of dangerous peroxides. 1 a V v Because of its solvent powers tetrahydrofuran is beginning to findwide application in industry. Some processes such as the laying-down of protective films and the production oftop coats and finishes require the evaporationof the solvent. ,Most other processes utilizing the material dissipate part, of the solvent through evapora; tion. Unless the resultant vapors can be recovered,- economic losses may become prohibitive. Use ofitetrahydrofuran as a solvent'is, however, somewhat, compli-f. cated by its tendency to form unstable or even explosive; peroxides .by reaction with oxygen. Such peroxides may result from, mere contact of the tetrahydrofuran, with air, particularly if the former is in the vapor state.

.Heretofore no safe procedure for the recovery of tetrahydrofuran vapors from air has, in fact, been available., Whenever the recovery was attempted peroxides were. formed and these on occasion resulted in explosions.,I-I.,. Rein, Angew. Chem. 62, 120 (1950),discusses the forma-,v tion of these peroxides and describes an explosion resulting therefrom. A mechanism yielding the peroxides. is, shown by Criegee in the same journal. Itis evident that. recovery of tetrahydrofuran vapors from air is attended by some risk. An additional problem derives frorhthe? fact thattetrahydrofuran and water form an azeotropic mixture thatQcannbt easily bev broken. The mixture... whichwcontains about. 5.3% water, possesses a boiling point of 63.4 ,-63.89,C. 3 Since the boiling point of tetr'ae. hydrofuran is. 65-f67 C. at standard pressure, the azeotropefiswthe first fraction collected on distillation. of tetrahydrofuran vapors condensed from moist air.

An object of this invention is therefore development. of a novel and usefulprocess for recovering tetrahyd'rofuran vapors from air. Another object is development of. a process for recovering tetrahydrofuranfrorn air withoutthe formation of dangerous peroxides. A further. object is development. of a process which can recover tetrahydrofuran-fromair and dry the recovered materiaL. Stillfurtherobjects will be evident from the remainder of 1 ;The-,abov'e-mentioned objectives can be" accomplished by a procedure which includes adsorbing tetrahydrofuran vapors mixed with air on activated charcoal containing iron; gstearningthe charcoal to recover tetrahydrofuraml and drying the tetrahydrofuran with n-pentane. A pre.-: liminary distillation-of the steam condensate to obtain the1azeotrope',ffourid in the. first fraction distilled, may be: employedtoayreducerthe amount of n-pentane required. 1 Several otherjvariations in procedure may be followedi assignor to E. I. (lu

Patented Apr. 30, 1957 formed. Such materials include those metals most closely resembling iron, that is cobalt and nickel. Iron is very Satisfactory and is preferred because it is present in some commercial charcoals. The iron, cobalt or nickel utilized will generally be in some combined form such as V an'oxide but the exact state of chemical combination is not considered critical. The quantity of metal present in the charcoal may vary from a minimumof about 15 p. p. m. to appreciable fractions of the adsorbant. Preferably charcoal containing about 75 p. p. m. iron is employed.

It is not absolutely essential that n-pentane be employed in the drying step since, as will be evident, other materials may be, substituted for it.- Since n-pentane is relativelycheap and quite eflicient, it is preferred.

There follow several examples which illustrate in more detail th'ewvarious aspects of this invention.

EXAMPLE 1 v activated' charcoals in the presence of air to determine Some of the the effect of the charcoal on peroxides. carbon contained iron while one sample did not. sults are set forth in Table Tdlile L -Pr coldt ion bf tetrahyllrofurari through charcoal ca bon sample A B o nonin sample (p. p. m.) 10-60 1, 000-10, 000 0 THE Peroxide (mg):

(1) In Origlnal'lHF so 140 so v(2) In Efiluent THF 1o 26 37 (3) Left in 0arb0n.. 16 3 50 (4) Deoomposed 54 112 0 Charcoals containing a very small quantity of iron will EXAMPLE 2 A series of runs was made by passing air containing tetrahydrofuran vapors through an adsorption column holding one pound of the charcoal called sample A above. Space velocity was varied between 0.8-6.8 l./l./min. and contact time of the air stream with the charcoal varied between 9 and 97 seconds. The concentration of tetrahydrofuran vapors used in the entire series ranged between 0.0l-l.9% by volume. j

The column was scrubbed with steam after each passage of the vapors therethrough and the steam-tetrahydrofuran mixture condensed. In some cases the condensate was then dried by distillation with n-pentane as noted below.

7 Results showing adsorption without the formation of Other-'fihelydivided. colloidal adsorbing agents such as peroxides are given by Table II.

T able II.-. 1ds0rpti0 n of tetrqhydrof uran on charcoal vapors Run; .4 1 2 3 4 5 THE vapor in air (percent by vol.).. 0. 8 0. 8 1. 9 0. 1.1 Relative humidity of air (room temp.) 0 0 40 40 Space velocity (LIL/min.) 2. 8 0.6 1. 1 8.0 4. 1 Linear velocity of gas (cm/sec.) 2. 7 0. 6 1. 1 6. 8 4. 0 Contact time vapors with carbon (see) 22 97 53 9 15 Totalweight of THF (g.) 84 164 89 133 103 THF-water azeotrope recovered (g)... 72 135 84 THF Peroxide (p. p. m.):

(1) In carbon before steaming 50 30 (2) In'carbon alter steaming 44. 6 41 g (3) In THF-steam condensate 0 G (4) In THF-water azeotrope 0 0 Table II shows that tetrahydrofunan vapors mixed with air can be recovered 'over charcoal containing iron without the formation of any peroxide. Concentration and drying of the steam distillate can then be carried out without danger. In this process it will be noted that such factors as the initial concentration of the tetrahydnofuran vapors in air, the space or linear velocity of the gas mixture, contact time and relative humidity are not critically important. The concentration of the vapors is however limited in practice by the fact that mixtures of air land tetrahydrofuran containing above about 2.1% of the organic material are explosive.

EXAMPLE 3 The steam condensates of Example 2 always give the tetrahydrofuran-water azeotrope on simple fractionation. If the azeotnope is distilled in the presence of n-pentane weighing 25-100% as much as the azeotrope, fractionation 'occurs and substantially anhydrous tetrahydrofuran separates. In practice the azeotrope may be first mixed with an equal volume of n-pentane. The mixture separates into a bottom water layer and a 'top organic layer. The water is :drawn off and the top layer can then easily be fractionated, any Water remaining after the mechanical separation passing off with the pentane. The effect of n-pentane on the azeotrope is shown by Table III.

Table [IL-Drying tetrahydrofuran with n-pentane 1 After n-pentane was distilled off. i Remainder was left in reused n-pcntane traction.

It will be seen that the volume of n-pen-tane utilized can be as small as one-half that of the tetrahy'drofuran wlater mixture. Larger amounts are of course efficacious but increase the costs of the distillation. Some other compounds such as ethanol, n-hexane, benzene, and cyclohexane may be substituted for n-penttane but none of these can be separated as easily from tetrahydr'ofuran. as can the n-pentane. In addition, formation of peroxides was greatly increased in the fractionation step by cyclohexane, necessitating the use of an inhibitor. The glycerol of Bremner et 211., British Patent 630,149 can also be substituted for n-pentane but, like the other substituents, is not as efficient as the pentane.

It is clear from the foregoing examples that adsorption of tetrahydrofuran vapors on charcoal containing only traces of iron compounds, steaming the charcoal after the adsorption; fractionating the condensate, adding n-pcntane to the azeotrope and fractionating the resulting pentanetetrahydrofuran mixture is an efficient method of recovering tetrahydrofuran for reuse as a solvent. N-pentlane can alternatively be added directly to the first steam condensate but, for reasons of economy, it may be preferred to fractionate the latter and add the pentane to the azeotrope alone.

The value of iron-containing charcoal with tetrahydrofuran is not limited to its use in the recovery process. Tetrahydrofuran can be stored over charcoal carrying traces of iron without formation of dangerous quantities of the peroxide. Thus te'trahydrofuran can be kept in la closed glass container with little or no air space for long periods of time if 5-25% by weight of the iron-containing charcoal is supplied thereto. Such a method of storage avoids use of soluble additives. Tetrahydrofuran can be separated from the charcoal by distillation or by mere filtration. Table IV shows the effect of adding charcoal containing iron to samples of tetrahydrofuran stored under identical conditions in a closed container with an air Having now described my invention, I claim:

1. The method of inhibiting the formation of peroxides in tetrahydrofuran which comprises contacting said tetrahydrofuran with a finely :divided inert carrier containing 10 to 10,000 p. p. m. of a metal chosen from the group consisting of iron, cobalt and nickel.

' 2. The method of inhibiting the formation of peroxides in tetrahydrofunan which comprises contacting the tetrahydrofuran with an adsorption agent for tetrahydrofuran containing 10 to 10,000 p. p. m. of iron. 1

3. The method of claim 2 in which the adsorption agent is activated charcoal and iron is present therein to the extent of about 15 to 75 p. p. m.

4. The method of claim 3 in which iron is present in the activated charcoal to the extent of about 75 p. p. m.

5. The process of recovering tetrahydrofuran from a mixture of the vapor thereof with air which comprises passing said mixture through an adsorption agent containing 10 to 10,000 p. p. m. of iron to decompose catalytically peroxides of tetrahydrofuran, passing steam through said adsorption agent following the mixture, condensing the steam after its passage through the adsorption agent and separating tetrahydrofuran from the resultant steam condensate.

6. The process of claim 5 in which the adsorption agent is activated charcoal.

7. The process of recovering tetrahydrofuran from a mixture of the vapor thereof with air which comprises passing said mixture through activated charcoal containing between about 15 p. p. tn. to about 75 p. p. m. of iron, passing steam through the charcoal following the mixture with air, condensing the steam after its passage through the charcoal and separating tetrahydrofuran from the resulting steam condensate.

8. The process of recovering tetrahydrofuran from a mixture of the vapor thereof with air which comprises passing said mixture through activated charcoal containing between about 15 p. p. m. to about 75 p. p. m. of iron, passing steam through the charcoal, condensing the steam after its passage through the charcoal, adding npentane to the resulting steam condensate, separating the organic and aqueous layers which form in said condensate upon the addition of n-pentane and fractionating the organic layer.

9. The process of claim 8 in which the n-pentane added to the condensate'weighs between about 25% and as much as the azeotrope.

10. The process of recovering tetrahydrofuran from a mixture of the vapor thereof with air which comprises passing said mixture through activated charcoal containing between about 15 p. p. m. and about 75 p. p. m. of iron, passing steam through said charcoal, condensing the steam after its passage through the charcoal, distilling the tetrahydrofuran-water azeotrope from the resulting steam condensate, adding n-pentane to said condensate and separating the organic and aqueous layers which form in the condensate after the addition of the n-pentane.

References Cited in the file of this patent UNITED STATES PATENTS Coleman Dec. 2, 1917 Reppe Aug. 5, 1941 Reppe Aug. 5, 1941 Bour Dec. 2, 1947 FOREIGN PATENTS Germany Oct. 20, 1943 France Ian. 29, 1945 

1. THE METHOD OF INHIBITING THE FORMATING OF PEROXIDES IN TETRAHYDROFURAN WHICH COMPRISES CONTACTING SAID TERAHYDROFURAN WITH A FINELY DIVIDED INERT CARRIER CONTAINING 10 TO 10,000P.P.M. OF A METAL CHOSEN FROM THE GROUP CONSISTING OF IRON, COBALT AND NICKEL. 